An immunity reaction is used to form an immunity complex for identifying an antibody or antigen in a biological sample such as serum or urine. When a solid phase and a liquid phase are made to react with each other, it is a general practice that a labeled antibody is used as a reagent and the liquid phase is measured using a detection element after the reaction. Radioisotopes, enzymes, colored particles, fluorescent substances, light-emitting (luminescent) substances or the like are known as the labeling substances.
In electrochemical luminescent flow-through cells according to prior arts, an excessive amount of luminescent reagent is added with respect to an amount of a measuring target in order to cause the luminescent reagent to be bound to a trace amount of the measuring target with a high probability, and therefore a large amount of the luminescent reagent (free component) which is not bound to the measuring target exists in a solution, resulting in a problem that a noise signal originating from the free component causes an SN ratio to deteriorate.
As a prior art, Patent Literature 1 discloses the following technique. That is, the patent literature includes a description that a magnet is placed outside a wall surface of a flow-through cell, a measuring target (hormone, tumor marker, drug, enzyme, cytokine, nucleic acid or the like) is held to magnetic beads via an antigen-antibody bond, the magnetic beads are held to the surface of a working electrode via a magnet, and a component which is not held to the surface of the working electrode and which is a noise originating component is washed away by the force of water flow to improve measuring accuracy. Separation between the component held to the surface of the working electrode (binding component (Bind; B)) and the component not held to the surface of the working electrode (free component (Free; F)) is called “B/F separation.”